this is from their website:
Your internal matchmaking rating (or, MMR) is adjusted after every match, not just when you get your Competitive Update—it goes up when you win a game and goes down when you lose a game. However, how much it goes up or down is based on a variety of factors surrounding that match. Here are the three most important factors:
- What is your skill rating compared to your opponents’ rating?
- How new are you to Overwatch?
- How frequently do you play that specific Competitive mode?
To address the first bullet, a player that can beat a stronger team will have a greater increase in their internal MMR rating. The stronger the average matchmaking rating (MMR) of your opponents, the more challenging it should be to win the match. While it is important to keep the average MMR rating of both teams as close as possible, very rarely are they precisely equal. We want to make sure that we can deliver fast queue times for everyone at all times, so sometimes there may be a greater difference between the two averages.
Secondly, your experience and how much you are keeping up with your skills are also important factors. When a player is brand new and qualifies to play in Competitive Play, our matchmaking system has very little information to assess their skill level. In most cases, we can get a broad understanding of their current skill in as little as five games, which aligns to their first Competitive Update, but this is just a broad estimate, which is why new players will see their skill tier and division change frequently.
This takes us to the third bullet point. The same can also apply to returning players who have been inactive for some time, which is one reason why we remove their skill tier/division if they didn’t play in that Competitive mode or role for a whole season. Inactive players will have their MMR lowered during their absence. We’ll also increase our uncertainty rating the longer the player is inactive. This uncertainty rating allows players to gain and lose MMR more quickly, so when the inactive player returns, they can jump back to their previous rank if they perform well, or they can lose MMR faster if their actual skill has decayed.
Whether you are a new player or someone returning to Overwatch 2 after an extended break, the key is to keep playing games. The more you play, the more information we will have, and the more confident the matchmaker will be about your current skill division and tier.
It’s these adjustments that change your MMR each game, and it’s with your current MMR that we determine what match is best for you every time you queue.